1. Field of the Invention
The present invention is directed to a method of filtering heavy hydrocarbon liquids containing particulate solids. More particularly, the invention is directed to a process for filtering coal liquefaction products to remove particulate ash and unconverted coal solids using fine metallic particle filter aid material, and for recovering the metallic filter aid for reuse in the filtration of coal liquefaction products.
2. Description of Prior Art
The use of filtration as a method for deashing coal liquefaction products is known. For example, U.S. Pat. No. 3,960,701 discloses a process for forming coke and electrode carbon from coal, in which coal-derived liquid is filtered using rotary drum and precoated thimble type filters. Also, U.S. Pat. No. 3,962,070 to Stotler discloses a process for the hydrogenation of coal in which unconverted coal solids are separated from the recycled residuum liquid using a liquid cyclone separator and a rotary drum type filter. Usually, a filter aid material, such as diatomite or volcanic ash particles, is mixed with the coal liquefaction product and the unconverted coal and ash solids are removed by filtration. By using a suitable filter aid material, it was found that rapid plugging of the filtering medium surface is avoided and adequate liquid filtration rates can be obtained.
Estimates have indicated that for coal liquefaction plants having 1,000,000 barrel per day total product capacity, the requirement for diatomite filter aid material would amount to a large percentage of the total diatomite production of the United States. Although regeneration and reuse of diatomite filter aid has been suggested, it has been found that the regenerated diatomite has a much lower effectiveness than the fresh material. Accordingly, there is a need for a filter aid material which can be regenerated simply and cheaply without decreasing significantly its effectiveness as a filter aid material, such filter aid material being suitable for use in the deashing of hydrocarbon liquid products from coal liquefaction processes.